How to setup multiple gateways for multiple Ethernets?

■ Purpose : Setup multiple gateways in linux
■ OS Environment : Linux [RHEL 5, 6]
■  Application : iproute package
■  Implementation Steps :
■  Assumption : eth0 has gateway 10.1XX.69.1 and eth3's gateway is 10.1XX.66.1.

Concept : Defining the gateway in two tables in conjunction with each interface.

1. Put entries in routing table :

echo "1 ISP1" >> /etc/iproute2/rt_tables
echo "2 ISP2 " >> /etc/iproute2/rt_tables

2.  Setup routing rules for  ISP1 table:

$ ip route add default via 10.1XX.69.1 dev eth0 table ISP1
$ ip rule add from 10.1XX.69.0/24 table ISP1


For the ISP2 table:

$ ip route add default via 10.1XX.66.1 dev eth3 table ISP2
$ ip rule add from 10.1XX.66.0/24 table ISP2

3. Make above rules persistent:

Put below entries in rc.local file  :

ip route add default via 10.1XX.69.1 dev eth0 table ISP1
ip rule add from 10.1XX.69.0/24 table ISP1
ip route add default via 10.1XX.66.1 dev eth3 table ISP2
ip rule add from 10.1XX.66.0/24 table ISP2

Note : You should replace the IP addresses in above commands.